/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.spelling.suggest;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.Collections;
import java.util.List;

import org.apache.lucene.analysis.Token;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.spell.Dictionary;
import org.apache.lucene.search.spell.HighFrequencyDictionary;
import org.apache.lucene.search.spell.SuggestMode;
import org.apache.lucene.search.suggest.FileDictionary;
import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.search.suggest.Lookup.LookupResult;
import org.apache.lucene.util.CharsRef;
import org.apache.lucene.util.IOUtils;

import org.apache.solr.common.util.NamedList;
import org.apache.solr.core.SolrCore;
import org.apache.solr.search.SolrIndexSearcher;
import org.apache.solr.spelling.SolrSpellChecker;
import org.apache.solr.spelling.SpellingOptions;
import org.apache.solr.spelling.SpellingResult;
import org.apache.solr.spelling.suggest.fst.FSTLookupFactory;
import org.apache.solr.spelling.suggest.jaspell.JaspellLookupFactory;
import org.apache.solr.spelling.suggest.tst.TSTLookupFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Suggester extends SolrSpellChecker {
	private static final Logger LOG = LoggerFactory.getLogger(Suggester.class);

	/**
	 * Location of the source data - either a path to a file, or null for the
	 * current IndexReader.
	 */
	public static final String LOCATION = "sourceLocation";
	/** Fully-qualified class of the {@link Lookup} implementation. */
	public static final String LOOKUP_IMPL = "lookupImpl";
	/**
	 * Minimum frequency of terms to consider when building the dictionary.
	 */
	public static final String THRESHOLD_TOKEN_FREQUENCY = "threshold";
	/**
	 * Name of the location where to persist the dictionary. If this location is
	 * relative then the data will be stored under the core's dataDir. If this
	 * is null the storing will be disabled.
	 */
	public static final String STORE_DIR = "storeDir";

	protected String sourceLocation;
	protected File storeDir;
	protected float threshold;
	protected Dictionary dictionary;
	protected IndexReader reader;
	protected Lookup lookup;
	protected String lookupImpl;
	protected SolrCore core;

	private LookupFactory factory;

	@Override
	public String init(NamedList config, SolrCore core) {
		LOG.info("init: " + config);
		String name = super.init(config, core);
		threshold = config.get(THRESHOLD_TOKEN_FREQUENCY) == null ? 0.0f
				: (Float) config.get(THRESHOLD_TOKEN_FREQUENCY);
		sourceLocation = (String) config.get(LOCATION);
		lookupImpl = (String) config.get(LOOKUP_IMPL);

		// support the old classnames without -Factory for config file backwards
		// compatibility.
		if (lookupImpl == null
				|| "org.apache.solr.spelling.suggest.jaspell.JaspellLookup"
						.equals(lookupImpl)) {
			lookupImpl = JaspellLookupFactory.class.getName();
		} else if ("org.apache.solr.spelling.suggest.tst.TSTLookup"
				.equals(lookupImpl)) {
			lookupImpl = TSTLookupFactory.class.getName();
		} else if ("org.apache.solr.spelling.suggest.fst.FSTLookup"
				.equals(lookupImpl)) {
			lookupImpl = FSTLookupFactory.class.getName();
		}

		factory = core.getResourceLoader().newInstance(lookupImpl,
				LookupFactory.class);

		lookup = factory.create(config, core);
		String store = (String) config.get(STORE_DIR);
		if (store != null) {
			storeDir = new File(store);
			if (!storeDir.isAbsolute()) {
				storeDir = new File(core.getDataDir() + File.separator
						+ storeDir);
			}
			if (!storeDir.exists()) {
				storeDir.mkdirs();
			} else {
				// attempt reload of the stored lookup
				try {
					lookup.load(new FileInputStream(new File(storeDir, factory
							.storeFileName())));
				} catch (IOException e) {
					LOG.warn("Loading stored lookup data failed", e);
				}
			}
		}
		return name;
	}

	@Override
	public void build(SolrCore core, SolrIndexSearcher searcher)
			throws IOException {
		LOG.info("build()");
		if (sourceLocation == null) {
			reader = searcher.getIndexReader();
			dictionary = new HighFrequencyDictionary(reader, field, threshold);
		} else {
			try {
				dictionary = new FileDictionary(new InputStreamReader(core
						.getResourceLoader().openResource(sourceLocation),
						IOUtils.CHARSET_UTF_8));
			} catch (UnsupportedEncodingException e) {
				// should not happen
				LOG.error("should not happen", e);
			}
		}

		lookup.build(dictionary);
		if (storeDir != null) {
			File target = new File(storeDir, factory.storeFileName());
			if (!lookup.store(new FileOutputStream(target))) {
				if (sourceLocation == null) {
					assert reader != null && field != null;
					LOG.error("Store Lookup build from index on field: "
							+ field + " failed reader has: " + reader.maxDoc()
							+ " docs");
				} else {
					LOG.error("Store Lookup build from sourceloaction: "
							+ sourceLocation + " failed");
				}
			} else {
				LOG.info("Stored suggest data to: " + target.getAbsolutePath());
			}
		}
	}

	@Override
	public void reload(SolrCore core, SolrIndexSearcher searcher)
			throws IOException {
		LOG.info("reload()");
		if (dictionary == null && storeDir != null) {
			// this may be a firstSearcher event, try loading it
			FileInputStream is = new FileInputStream(new File(storeDir,
					factory.storeFileName()));
			try {
				if (lookup.load(is)) {
					return; // loaded ok
				}
			} finally {
				IOUtils.closeWhileHandlingException(is);
			}
			LOG.debug("load failed, need to build Lookup again");
		}
		// loading was unsuccessful - build it again
		build(core, searcher);
	}

	static SpellingResult EMPTY_RESULT = new SpellingResult();

	@Override
	public SpellingResult getSuggestions(SpellingOptions options)
			throws IOException {
		LOG.debug("getSuggestions: " + options.tokens);
		if (lookup == null) {
			LOG.info("Lookup is null - invoke spellchecker.build first");
			return EMPTY_RESULT;
		}
		SpellingResult res = new SpellingResult();
		CharsRef scratch = new CharsRef();
		for (Token t : options.tokens) {
			scratch.chars = t.buffer();
			scratch.offset = 0;
			scratch.length = t.length();
			List<LookupResult> suggestions = lookup.lookup(scratch,
					(options.suggestMode == SuggestMode.SUGGEST_MORE_POPULAR),
					options.count);
			if (suggestions == null) {
				continue;
			}
			if (options.suggestMode != SuggestMode.SUGGEST_MORE_POPULAR) {
				Collections.sort(suggestions);
			}
			for (LookupResult lr : suggestions) {
				res.add(t, lr.key.toString(), (int) lr.value);
			}
		}
		return res;
	}
}
